Device and method for measuring effect of soiling on photovoltaic device

ABSTRACT

The device and method for measuring the effect of soiling on a photovoltaic device includes a device in which a photovoltaic device (reference solar cell, solar cells, PV module, etc.) may be shifted between partially and fully enclosed compartments in quick succession for measurements of the same device (1) when directly exposed to illumination or solar radiation; (2) when placed under a glass or transparent cover maintained cleared or cleaned of soil; and (3) when placed under glass or transparent cover left exposed to natural outdoor soiling, or attenuated using simulated soil that is not periodically cleaned. The measurements may be of short circuit current (Isc), maximum power (Pmax), or other electrical parameter conventionally used to evaluate performance of the photovoltaic device. A soiling ratio calculated as: 
               SR   Pmax     =     1   -         P     max   ⁢           ⁢   2       -     P     max   ⁢           ⁢   3           P     max   ⁢           ⁢   1                 
or calculated as:
 
               SR   Isc     =     1   -         I     sc   ⁢           ⁢   2       -     I     sc   ⁢           ⁢   3           I     sc   ⁢           ⁢   1                 
may be used to compare or monitor performance of the photovoltaic device between measurement cycles.

BACKGROUND 1. Field

The present disclosure relates to measuring and testing of photovoltaicdevices, and particularly to a device and method for measuring theeffect of soiling on a photovoltaic device, such as a reference cell, asolar cell, or a photovoltaic module, to determine the change inelectrical characteristics resulting from accumulated dust and otherenvironmental contamination.

2. Description of the Related Art

One form of energy generation is the conversion of sunlight toelectricity using a photovoltaic (PV) module that consists ofelectrically connected solar cells. When a group of modules are furtherconnected, a PV system is formed, which typically ranges in size fromresidential to utility.

When PV systems are installed in outdoor locations, one of the mostdetrimental environmental factors that affects their performance is theaccumulation of soil, which is the settlement of dust particles, debris,and/or other contaminants on the surface of PV modules, otherwise knownas soiling. Performance degradation occurs because when particles settleon the surface of PV modules, they interfere with incoming light byblocking, attenuating, and/or scattering it. The power output that islost as a result is known as the Soiling Loss (SL). Many research groupsin dust-intensive regions have reported SL values well above 20%. Forexample, a PV system that was installed in a desert region tilted at20°, lost up to 60% of its power after six months of no cleaning.

Such high soiling loss values result in significant revenue deficienciesand excessive operation and maintenance costs. Consequently, there hasbeen a growing interest in quantifying and monitoring such anenvironmental factor, as the deployment of PV systems in dust-intensiveclimates is rapidly increasing. This is especially true for utilityscale PV systems, as it improves energy prediction models, optimizes PVPlant cleaning strategies, and creates a new performance assessmenttool.

Fundamentally, existing soiling detectors are implemented by measuringone of three primary parameters, viz., soil mass; light transmission; orPV performance. The latter parameter has been widely adopted by PVpractitioners and researchers for directly measuring the power loss dueto soiling. This method of soiling detection measurement involvescomparing the power output of an installed reference PV device (i.e.,cleaned daily) to a test PV device (i.e., left to naturally soil).

Although performance-based measurements using two PV devices offer adirect way to measure SL, the method involves high uncertainty, since itassumes that the two devices are identical. However, it is wellestablished that PV devices fabricated using the same materials andprocesses have intrinsic differences. Such differences include (a)Quantum efficiency (QE); (b) Angular response (Ar); (c) Thermal response(Tr); (d) Parasitic resistances (Pr); and how these four parameterschange over time.

Therefore, simply comparing two PV devices to measure soiling whileneglecting the aforementioned differences will introduce highmeasurement uncertainty. Using this method, errors as high as 4.5% havebeen reported. Although a few researchers have considered accommodatingsuch factor's, their approaches require intensive periodic in-lab PVassessment, which renders them impractical for long-term monitoring.Furthermore, such an assessment is less than optimum for accommodatingthe particular environment of a given installation site. Thus, a morepractical, reliable, and accurate soiling measurement device and methodsolving the aforementioned problems are desired.

SUMMARY

The device and method for measuring the effect of soiling on aphotovoltaic (PV) device are used to provide data representative ofdeterioration in performance from soiling of PV devices. A test jig witha test enclosure having first, second and third measurement stations canbe used. In this embodiment, the first station is substantially externalto the test enclosure and is used to obtain reference values for a PVdevice as a device under test (DUT); this station will beinterchangeably referred to as the initial state hereinafter. The secondand third stations are within a test enclosure. A support for the DUThas the capability of transporting the PV device between the first,second and third stations for sequential testing on the same deviceunder different conditions. At the first station, the DUT hassubstantially full, direct, unobstructed exposure to a light source,defining a first state. At the second station, the DUT has exposurethrough a transparent cover of the enclosure that is maintained in cleancondition, defining a second state. In this regard, the transparentcover of the second compartment is adapted for a wide range of cleaningfrequency (minutely, hourly, daily, etc.) At the third station, the DUThas exposure through a transparent cover of the enclosure that has beenexposed to natural outdoor soiling, or attenuated using simulated soil,defining a third state. In the first state, the exposure comprises lightpassed directly to the PV device, substantially without passing throughthe enclosure. In the second state, the exposure comprises light passedto the PV device through the transparent cover in a clean state. In thethird state, the exposure comprises light passed to the photovoltaicdevice through a transparent cover in a soiled state. A measuring andtest unit is configured to measure short circuit current (Isc), maximumpower (Pmax), and/or other criteria in the three states in quicksuccession and report the result in a novel ratio to show the loss incurrent or power resulting from soiling conditions. The device may becomputerized to monitor changes in the ratio and/or store and manipulatedata relating to the efficiency of the PV device under test. Thedisclosed technology serves as a platform for PV device testing undersoiling conditions. It can accommodate any mono-facial PV technology,thus allowing for a wide range of potential applications.

These and other features of the present disclosure will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a device for measuring the effect ofsoiling on a photovoltaic device, shown in its east-west (E-W) lateralorientation and largely schematic.

FIG. 1B is a perspective view of a device for measuring the effect ofsoiling on a photovoltaic device, shown in its north-south (N-S) axialorientation and largely schematic.

FIG. 2 is a flowchart showing mechanical steps in taking of measurementsin three measurement states in a measurement cycle.

FIGS. 3A, 3B, and 3C are a flowchart showing the steps in a method formeasuring the effect of soiling on a photovoltaic device.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device and method for measuring the effect of soiling on aphotovoltaic (PV) device includes a device in which a PV device (solarcell, PV module, etc.) may be shifted between partially and fullyenclosed compartments in quick succession for measurements of the samedevice (1) when directly exposed to illumination or solar radiation; (2)when placed under a transparent cover maintained cleared or cleaned ofsoil; and (3) when placed under transparent cover left exposed tosoiling that is not periodically cleaned. The measurements may be ofshort circuit current (Ise), maximum power (Pmax), and/or otherparameters conventionally used to evaluate performance of the PV device.Each measurement may be an instantaneous value, or a measurement ofchanging values over a predetermined time interval, e.g., an I-V curve.A soiling ratio calculated as:

${SR}_{Pmax} = {1 - \frac{P_{\max\; 2} - P_{\max\; 3}}{P_{\max\; 1}}}$or calculated as:

${SR}_{Isc} = {1 - \frac{I_{{sc}\; 2} - I_{{sc}\; 3}}{I_{{sc}\; 1}}}$may be used to compare or monitor effectiveness of the PV device betweenmeasurement cycles.

To capture the soiling effect using a single device, the PV device isrequired to be measured under three different states. State 1 will bethe initial state where the Isc, Pmax, and/or other parameters of the PVdevice are measured. The device will then move to State 2 and a similarmeasurement to initial state, State 1, will be taken under a cleantransparent cover. For the final state, State 3, the same measurementwill be repeated under a soiled (i.e., never cleaned) transparent cover.Because the extra layer of transparent cover in States 2 and 3 willintroduce an additional power loss, measurements in all 3 states need tobe mathematically compensated for this extra layer. To further ensureaccuracy, all three states will be measured in a sufficiently shortperiod of time. Any deviations in PV temperature and/or amount ofsunlight received from the states will be normalized. This processallows for the computation of the Soiling Ratio (SR) as an indicator ofPV performance loss resulting from soiling. Since the new disclosedtechnology utilizes a single PV device, the SR will be expressed as:

${SR}_{Pmax} = {{1 - \frac{P_{\max\mspace{11mu}{dirty}}}{P_{\max\mspace{11mu}{clean}}}} = {\frac{P_{\max\; 3} + \left( {P_{\max\; 1} - P_{\max\; 2}} \right)}{P_{\max\; 1}} = {1 - \frac{P_{\max\; 2} - P_{\max\; 3}}{P_{\max\; 1}}}}}$and/or as:

${{SR}_{Isc} = {\frac{I_{{sc}\; 3} + \left( {I_{{sc}\; 1} - I_{{sc}\; 2}} \right)}{I_{{sc}\; 1}} = {1 - \frac{I_{{sc}\; 2} - I_{{sc}\; 3}}{I_{{sc}\; 1}}}}},$where SR is the Soiling Ratio, P_(max) is the power at maximum powerpoint, I_(sc) is the short circuit current, and the subscripts 1, 2, and3 refer to the State in which the measurement was made.

The use of a single PV device minimizes uncertainties stemming fromcomplex differences that inherently exist between two similar, butnonidentical devices. This provides a low-cost technique offeringpractical in-field use because it does not require cumbersome periodicoperation and maintenance cycles. Furthermore, for an accurate soilingrepresentation of a PV system, the user is not confined to a limited setof PV technologies (i.e., some products supply only one type), butbroadens the scope of work to accommodate any desired mono-facialtechnology. Ultimately, the technique is intended to provide a reliable,practical, and affordable soiling monitoring system for widespreadapplications that extend from research to industry. In particular, thistechnique advances the optimization of PV cleaning cycles and cost,monitoring energy production losses due to soiling, studying theeffectiveness of new anti-soiling surface coatings, and the collectionof site-specific data.

According to the method, three consecutive Isc, Pmax, and/or otherparameter measurements of the PV device are taken, first, under notransparent cover (State 1), then under a clean transparent cover (State2), and finally under a soiled transparent cover (State 3). Thesemeasurements can be achieved in a sufficiently short period of time.Measuring one PV device can effectively eliminate the uncertaintiesstemming from two nonidentical devices. The disclosed technology can bea standalone system where no external power supply is needed to allowinstallation in remote areas.

Software may be provided to enable the user to monitor and control thesensor system. Features such as data analysis, data presentation, anddata extraction can be included because the use of a direct calculationof soiling loss. As part of the data acquisition system, software may beprovided in any convenient form, such as a desktop, as web-basedsoftware, or using a handheld device. The software can also beintegrated with the data acquisition system. The system may executefunctions including, but not limited to, the following: receive data ofphysical variables; process data; provide a graphical user interface;offer analytic tools for researchers and industry; forecast and computeoptimal cleaning time; export records and reports in text or otherportable data formats; detect system faults; configure features ofsystem hardware, such as motor and fan speeds; and integrate withstandard SCADA systems for PV power plants.

In addition to the above-mentioned features, the software will havebuilt-in features that would allow a user, such as an administrator, tochange the way data is organized, computed, and filtered, which allowsfor device optimization.

FIGS. 1A and 1B are schematic diagrams of a device 101 configured formeasuring the effect of soiling on a photovoltaic device, shown in alateral configuration and in an axial configuration, respectively In thelatter configuration, the PV device is measured along the north-southdirection rather than the east-west direction between states, whichyields higher measurement accuracy and allows for new parameters to beevaluated. Depicted is a frame housing 111 for testing a PV device, suchas a PV module component 113, as a device under test (DUT). The device101 has three test stations, 121, 122, 123, corresponding to threemeasurement states, State 1—initial, State 2—clean and State 3—soiled.Test station 121 is only partially enclosed, being exposed directly tothe outside environment for receiving illumination or solar radiation,whereas test stations 122 and 123 are provided as an enclosedcompartment portion 127 of the device 101. A transparent cover 130, suchas a tempered PV glass, forms a top of enclosed portion 127. It isnoted, however, that, at test station 123, the transparent cover 130 issoiled without any cleaning throughout the soiling monitoring cycle. TheDUT 113 can be removed from its housing so that it can be characterizedeither by its OEM or by an independent laboratory, when needed.

Nevertheless, the device 101 can be used to compare operationalparameters in the three states, provided care is taken to not damage theDUT 113 during routine testing. In the device 101, the DUT istransported through stations 121, 122, and 123 to measure the electricaloutput at each station in a sufficiently short period of time such thatenvironmental variations between the three measurements are kept to aminimum.

As can be seen in FIG. 1A, the DUT component 113 is shown outside of anenclosed portion of the device 101, but still supported by the device101 at test station 121, corresponding to “State 1—initial”. Both theDUT component 113 and the tray 135 holding it are coplanar with theother testing stations 122 and 123.

The DUT component 113 is then moved inside the device 101 to teststation 122. Test station 122 is within the enclosed portion of thedevice 101, under a portion of the device 101 (a transparent cover 130)maintained in a clean state. Testing at test station 122 corresponds to“State 2—clean”. In the enclosed portion of the device 101, light passesthrough a transparent cover 130, which, at test station 122, ismaintained in a substantially clean condition.

The DUT component 113 is then moved inside the device 101 to teststation 123. Test station 123 is within the enclosed portion 127 of thedevice 101, under a portion of the device 101 left in a soiled state.Testing at test station 123 corresponds to “State 3—soiled”.

While a single enclosure is shown for test stations 122 and 123, it isunderstood that test stations 122 and 123 may be provided with separateenclosures, each with a separate transparent cover 130, but with station123 in a soiled state. Likewise, a single test station can be used toprovide the test operations of test stations 121, 122 and 123 with asingle PV device, with the test station being changed by uncovering theDUT for State 1, covering the DUT with the clean transparent cover forState 2, and covering the DUT with the same or a different cover, but ina soiled state, for State 3.

The “State 3—soiled” condition can be adapted to outdoor localconditions. Examples of environmental debris or contamination can bedust from wind, vegetation debris, and soiling from birds or animalwaste, all of which can vary according to the location of the test site.

The device 101 may have a support tray 135, which can be used totransport the DUT between the test stations, 121, 122, 123, eithermanually or automatically.

The device 101 is used to determine a performance difference between aclean state, described as “State 2—clean”, and a soiled state, describedas “State 3—soiled”. The device 101 can then be used to determine thedifference in electrical output when a PV device's surface becomessoiled.

Ventilation fans (not separately shown) may be used to reduce heatbuildup until internal temperature and humidity sensor readingssubstantially agree with the ambient. When the DUT is at rest, and nomeasurements are being taken, the ventilation fans may operate toprotect the internal components of the device 101 inside the enclosedcompartment portion 127. Further, the enclosed compartment portion 127can be opened for scheduled and unscheduled maintenance. The cleaning ofthe transparent cover 130 may be done either manually or automaticallyusing a built-in washer 140.

The device 101 has a tilting mechanism component 114, which can adjustthe tilt angle of test stations, 121, 122, 123, the tray component 135,and the DUT component 113 concurrently between 0° (i.e., parallel to theground) to 90° (i.e., perpendicular to the ground) either manually orautomatically.

FIG. 2 is a flowchart showing one variation of the mechanics of takingmeasurements in States 1, 2 and 3. In each test sequence, testing isperformed for short circuit current (Isc), maximum power (Pmax), and/orother criteria of the DUT component 113. Environmental data is alsotaken.

Referring to FIG. 2, the DUT is initially placed in a position outsidethe enclosure 127 of the device 101, and the test station 122 iscleaned, if needed (step 201). Measurement 1 is then taken (step 203).The DUT is then moved (step 205) into the enclosure 127 of the device101 at test station 122 for testing in a clean state, as Measurement 2.The difference is that substantially all factors imposed by enclosingthe DUT in enclosure 127 are present. The DUT is then tested (step 207).The DUT is then moved (step 211) for testing (step 215) in a soiledstate, as Measurement 3. In the soiled state, the device's 101 thirdtest station 123 is either naturally soiled with dust and otherenvironmental debris, or simulated dirt can be used at test station 123,and measurements are taken under those conditions (step 215), which isMeasurement 3.

In an automated process, the DUT is placed in a position outside theenclosure of the device 101, and automated movement is achieved by motorcontrols to move the support tray 135. The support tray 135 transportsthe DUT for measurements 1, 2, and 3 (with measurement 1 performedbefore movement). This provides an automated acquisition of measurementsfor each test station where the DUT is evaluated.

On completion of the measurements, after obtaining Measurement 3 (step215), the DUT is moved (step 217) to rest either at station 1, station2, or remain at station 3 between measurement cycles.

One difference between Measurements 1 and 2 is that a baseline isestablished to account for losses due to the construction of the device101 itself. In that way, the measurements taken under the regimes ofMeasurements 2 and 3 represent the changes resulting from the soilingrepresented by Measurement 3, with the effects of the device 101cancelled out by the difference between Measurements 1 and 2.

FIGS. 3A-3C are flowcharts showing the procedures and set-up requiredfor obtaining soiling measurements when using a single PV device. Theprocess comprises of pre-installation 301, field measurements and dataacquisition 302, normalizing weather conditions to a reference state 303(i.e. state 2), and computation of soiling ratio (SR) 304.

In the pre-installation step 301, a determination (step 311) is made ofthe ability to measure the PV device's alpha, beta, Rs and k values.Ideally, these values can be measured in the lab (in-house measurements)in accordance to IEC 60904. If it is not possible to obtain some ofthese measurements, a determination (step 312) is made as to whethermeasurements can be obtained from other accredited labs or supplied fromanother source. In either case, if these measurements cannot be made,then manufacturer-supplied parameters are used (step 315). If thesevalues can be measured, then the device parameters are measured (step316). Similarly, if some, but not all, parameters can be measured, thenthese parameters are used in combination with manufacturer-suppliedparameters.

The parameters are provided for use in field measurements and dataacquisition 302. Three measurements are used to obtain values for States1, 2 and 3. In State 1, the measurement is taken with no transparentcover and the DUT is substantially clean (step 321). In State 2, ameasurement is taken with clean transparent cover (step 322), and inState 3, a measurement is taken with soiled transparent cover (step323). The measured data is organized into a standard format (step 327).

After obtaining the data for each of States 1, 2 and 3, normalized 303for weather conditions, a computation is made of a soiling ratio. In thenormalization according to weather conditions 303, adjustments are madeso that weather conditions as would affect the measurements are takenfor State 2. These same adjustments are then applied to States 1 and 3.The normalized data is re-organized into a standard format (step 367)for use in the process for computing the soiling ration (SR) 304.

Additional functions may be implemented within the scope of thisdisclosure, which may comprise combining an automatization capability toperiodically clean the “clean transparent cover” (required step) inaddition to manual cleaning; providing an ability to both manually andautomatically move the PV device from State 1, 2, and 3; development ofuniversal design to accommodate all PV sizes; combining the device witha weather station; moving the transparent cover of stations 2 and 3 overthe fixed DUT at station 1 to make the three sequential measurementsrequired; and combining the device with a solar simulator for indoortesting

It is to be understood that the device and method for measuring theeffect of soiling on a PV device are not limited to the specificembodiments described above, but encompasses any and all embodimentswithin the scope of the generic language of the following claims enabledby the embodiments described herein, or otherwise shown in the drawingsor described above in terms sufficient to enable one of ordinary skillin the art to make and use the claimed subject matter.

We claim:
 1. A method for measuring effects of soiling on a photovoltaicdevice, comprising the steps of: making three separate measurements ofat least one electrical parameter of a single photovoltaic devicecorresponding to the photovoltaic device's effectiveness in generatingelectricity in response to exposure to illumination, the measurementsbeing made sequentially in a single measurement cycle, the measurementsincluding a first measurement made with the photovoltaic deviceunobstructed and exposed directly to illumination, a second measurementmade with the photovoltaic device disposed in a compartment exposed toillumination through a transparent cover cleaned regularly, and a thirdmeasurement made with the photovoltaic device disposed in a compartmentexposed to illumination through a transparent cover on which natural orsimulated soil is permitted to accumulate without cleaning; andcomparing the three measurements to determine effects of soiling on thephotovoltaic device.
 2. The method for measuring effects of soiling on aphotovoltaic device according to claim 1, wherein the second and thirdmeasurements are made in compartments exposed to illumination through atempered photovoltaic (PV) glass cover.
 3. The method for measuringeffects of soiling on a photovoltaic device according to claim 1,wherein the at least one electrical parameter is maximum power, themethod further comprising the step of calculating:${SR}_{Pmax} = {1 - \frac{P_{\max\; 2} - P_{\max\; 3}}{P_{\max\; 1}}}$where SR_(Pmax) is a Soiling Ratio calculated from measurements ofmaximum power and P_(max1), P_(max2), and P_(max3) are measurements ofmaximum power from the first, second, and third measurements,respectively.
 4. The method for measuring effects of soiling on aphotovoltaic device according to claim 3, further comprising the step ofcalculating a soiling loss indicator (SL), wherein SL=(1−SR_(Pmax)). 5.The method for measuring effects of soiling on a photovoltaic deviceaccording to claim 1, wherein the at least one electrical parameter isshort circuit current, the method further comprising the step ofcalculating:${SR}_{Isc} = {1 - \frac{I_{{sc}\; 2} - I_{{sc}\; 3}}{I_{{sc}\; 1}}}$where SR_(Isc) is a Soiling Ratio calculated from measurements of shortcircuit current and I_(sc1) I_(sc2), and I_(sc3) are measurements ofshort circuit current from the first, second, and third measurements,respectively.
 6. The method for measuring effects of soiling on aphotovoltaic device according to claim 5, further comprising the step ofcalculating a soiling loss indicator (SL), wherein SL=(1−SR_(Isc)). 7.The method for measuring effects of soiling on a photovoltaic deviceaccording to claim 1, wherein the step of making three separatemeasurements of at least one electrical parameter further includes foreach of the measurements, measuring and test circuit testing for currentat maximum power (Imp), voltage at maximum power (Vmp), Maximum PowerPoint (MPP), and short circuit output current (Isc).
 8. The method formeasuring effects of soiling on a photovoltaic device according to claim7, further comprising the step of, for each of the measurements,plotting a current-voltage (IV) curve of the single photovoltaic device.9. The method for measuring effects of soiling on a photovoltaic deviceaccording to claim 1, further comprising the steps of: in apre-installation step, determining an ability to measure predeterminedparameters characterizing the photovoltaic device; using the measuredvalues or supplied values of the parameters for use in fieldmeasurements and data acquisition, and obtaining or using a value for aState 1, taken with no glass and no soil as an initial value, taking ameasurement for a State 2, taken with clean glass, and taking a valuefor a State 3, in a soiled state, with naturally or simulated soiledglass; providing the measured data in a standard format; normalizing themeasured electrical differences due to weather condition variations,with the normalizing applied to States 1, 2 and 3; and computing asoiling ratio (SR).
 10. The method for measuring effects of soiling on aphotovoltaic device according to claim 1, wherein the step of makingthree separate measurements of an electrical parameter comprises makingthe three measurements in quick succession to minimize PV temperatureand irradiance deviations between the measurements.
 11. A device formeasuring effects of soiling on a photovoltaic device, comprising: ahousing defining: a first partially enclosed compartment adapted forsupporting the photovoltaic device under test, the first partiallyenclosed compartment being exposed directly to illumination of thephotovoltaic device under test without any cover or obstruction; asecond enclosed compartment adapted for supporting the photovoltaicdevice under test, the second enclosed compartment having a transparentcover providing for illumination of the photovoltaic device under test,the transparent cover of the second compartment being adapted for a widerange of cleaning frequency; and a third enclosed compartment adaptedfor supporting the photovoltaic device under test, the third enclosedcompartment having a transparent cover providing for illumination of thephotovoltaic device under test, the transparent cover of the thirdcompartment being adapted for permitting natural or simulated soil toaccumulate on the transparent cover; a test circuit configured formeasuring an electrical parameter of the photovoltaic devicecorresponding to the photovoltaic device's effectiveness in generatingelectricity in response to exposure to illumination; and a controlcircuit connected to the test circuit for controlling the test circuitto make three measurements of the electrical parameter sequentiallywhile the photovoltaic device under test is in the first compartment,the second compartment, and the third compartment, respectively; and atilt mechanism which can adjust the tilt angle of the first partiallyenclosure compartment, the second enclosed compartment, the thirdenclosed compartment, and the photovoltaic device concurrently between0° to 90° either manually or automatically.
 12. The device for measuringeffects of soiling on a photovoltaic device according to claim 11,wherein the transparent cover of said second compartment and thetransparent cover of said third compartment each comprise temperedphotovoltaic (PV) glass.
 13. The device for measuring effects of soilingon a photovoltaic device according to claim 11, wherein the electricalparameter is maximum power, the test circuit being configured formeasuring maximum power, the control circuit being further configuredfor calculating:${SR}_{Pmax} = {1 - \frac{P_{\max\; 2} - P_{\max\; 3}}{P_{\max\; 1}}}$where SR_(Pmax) is a Soiling Ratio calculated from measurements ofmaximum power and P_(max1), P_(max2), and P_(max3) are measurements ofmaximum power in the first, second, and third compartments,respectively.
 14. The device for measuring effects of soiling on aphotovoltaic device according to claim 13, wherein the control circuitis further configured for calculating a soiling loss indicator (SL),wherein SL=(1−SR_(Pmax)).
 15. The device for measuring effects ofsoiling on a photovoltaic device according to claim 11, wherein theelectrical parameter is short circuit current, the test circuit beingconfigured for measuring short circuit current, the test circuit beingfurther configured for calculating:${SR}_{Isc} = {1 - \frac{I_{{sc}\; 2} - I_{{sc}\; 3}}{I_{{sc}\; 1}}}$where SR_(Isc) is a Soiling Ratio calculated from measurements of shortcircuit current and I_(sc1), I_(sc2), and I_(sc3) are measurements ofshort circuit current from the first, second, and third measurements,respectively.
 16. The device for measuring effects of soiling on aphotovoltaic device according to claim 15, wherein the control circuitis further configured for calculating a soiling loss indicator (SL),wherein SL=(1−SR_(Isc)).
 17. The device for measuring effects of soilingon a photovoltaic device according to claim 11, wherein said testcircuit and said control circuit are further configured for measuringand test circuit testing for current at maximum power (Imp), voltage atmaximum power (Vmp), Maximum Power Point (MPP) and, short circuit outputcurrent (Ise), and for plotting a current-voltage (IV) curve of thesingle photovoltaic device for each of the three measurements.
 18. Thedevice for measuring effects of soiling on a photovoltaic deviceaccording to claim 11, further comprising: at least one temperaturesensor selected from the group consisting of a thermocouple and aresistance temperature detector, the at least one temperature sensorbeing connected to said controller circuit; and at least one irradiancesensor selected from the group consisting of a pyranometer and areference PV device, the at least one irradiance sensor being connectedto said controller circuit; wherein said controller circuit isconfigured for controlling said test circuit to make the threemeasurements in quick succession to minimize PV temperature andirradiance deviations between the measurements.
 19. The device formeasuring effects of soiling on a photovoltaic device according to claim18, wherein said controller circuit is configured for normalizing themeasured data for temperature, weather and other ambient conditions. 20.The device for measuring effects of soiling on a photovoltaic deviceaccording to claim 11, further comprising a washing unit mounted on saidhousing and connected to said controller circuit, the controller circuitbeing configured to activate the washing unit to: wash the photovoltaicdevice when in the first partially enclosed compartment and to wash thetransparent cover of the second enclosed compartment with sufficientfrequency to ensure accurate measurement; and wash the transparent coverof the third enclosed compartment to reset the soiling monitoring cycle.